1. Field of the Invention
Aspects of the present invention relate to an optical disk apparatus and a method of driving the same and, more particularly, to a near-field optical disk apparatus and a method of driving the same to prevent a light focusing element and a disk from colliding with each other due to overshoot generated during a gap pull-in operation.
2. Description of the Related Art
Recently, a near-field optical disk apparatus to achieve a high data transfer rate has been proposed. Near-field optical disk apparatuses are also referred to as near-field recording systems. A near-field optical disk apparatus records data on a disk or reproduces data recorded on the disk using light in a near-field where diffraction of light does not occur. Accordingly, the near-field optical disk apparatus is required to control a gap distance between the end surface of a solid immersion lens (SIL) attached to a light focusing element, such as an object lens, and an optical disk such that the gap distance becomes very small. Generally, this gap distance corresponds to half the wavelength of an input laser beam. For example, the gap distance may be approximately 200 nm when a celadon laser having a wavelength of 400 nm is used.
In a near-field optical disk apparatus, an optical disk absorbs some of the incident light. Thus, the intensity of reflected light is reduced in a near-field state in which an actuator is moved towards the optical disk. This reduction of the intensity of reflected light as the actuator is moved towards the optical pickup decreases a gap error signal. When the gap error signal reaches a target point, the near-field optical disk apparatus performs a focus pull-in operation. The focus pull-in operation may also be referred to as a gap pull-in operation because the focus pull-in operation performed by the near-field optical disk apparatus may include performing a gap pull-in operation.
When the gap pull-in operation is performed, overshoot may be generated. This overshoot is generated due to the momentum of the actuator when an initial gap servo operation is performed in an operation of controlling a gap according to the intensity of light reflected from a disk to a SIL due to the near-field effect. Overshoot of less than several μm is not a problem in a conventional optical disk system. However, a similar amount of overshoot causes the disk and the SIL to collide with each other in a near-field optical disk apparatus.